MINOR: threads: report the number of thread groups in build options

haproxy -vv shows the number of threads but didn't report the number
of groups, let's add it.
diff --git a/src/thread.c b/src/thread.c
index c846229..64ac476 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -1066,8 +1066,8 @@
 
 	thread_cpus_enabled_at_boot = thread_cpus_enabled();
 
-	memprintf(&ptr, "Built with multi-threading support (MAX_THREADS=%d, default=%d).",
-		  MAX_THREADS, thread_cpus_enabled_at_boot);
+	memprintf(&ptr, "Built with multi-threading support (MAX_TGROUPS=%d, MAX_THREADS=%d, default=%d).",
+		  MAX_TGROUPS, MAX_THREADS, thread_cpus_enabled_at_boot);
 	hap_register_build_opts(ptr, 1);
 
 #if defined(DEBUG_THREAD) || defined(DEBUG_FULL)